There is a need for equipment for generating steam by use of fuel such as a high sulfur coal. Systems adapted to burn high sulfur coal by way of fluidized beds have been proposed heretofore. For example, see U.S. Pat. Nos. 3,387,490 and 3,763,830. The systems disclosed by said patents have not been widely adopted since they lack a number of control features and have several disadvantages.
In connection with a fluidized bed, said prior art systems use an upshot grid for discharging the fluidizing gas upwardly toward the bed. A downshot grid discharges the fluidizing gas downwardly in a direction away from the bed. Per se, a downshot grid is known. For example, see the downshot grid in U.S. Pat. No. 3,904,548. Downshot grids such as that disclosed in the last-mentioned patent are not practical for use in the individual combustion chambers of a combustor, do not facilitate removal of the grid in any one chamber for purposes of repair, and otherwise lack features of the present invention.